Semiconductor device adapted for imaging bar code symbols

ABSTRACT

A semiconductor device for imaging optical code symbols comprises no more than 1024 pixels, wherein each of the pixels has an aspect ratio that is greater than 2 to 1 with a short dimension not greater than 4 μm and not less than 2 μm, wherein preferably the pixels are arranged in a single row. The semiconductor may have a collection surface configured as a set of no less than 256 and no more than 1024 pixels. Also provided is a bar code reader including a sensor for imaging a field of view of the reader comprising a single semiconductor device as described above.

REFERENCES TO RELATED APPLICATIONS

This application is a continuation-in-part application which claims thebenefit of priority to U.S. patent application Ser. No. 10/118,562,filed Apr. 9, 2002. This application is also related to U.S. patentapplication Ser. No. 09/880,906, filed Jun. 1, 2001. This application isalso related to U.S. patent application Ser. No. 10/191,970, filed Jul.8, 2002, entitled Bar Code Reader Including Linear Sensor Array AndHybrid Camera And Bar Code Reader” of Patel, et al.

BACKGROUND OF THE INVENTION FIELD OF INVENTION

The present invention relates to semiconductor devices adapted forimaging optical code symbols, in particular bar code symbols, and to barcode readers including such a semiconductor device.

Optical codes are patterns made up of image areas having different lightreflective or light emissive properties, which are typically assembledin accordance with a priori rules. The term “bar code” is sometimes usedto describe certain kinds of optical codes. The optical properties andpatterns of optical codes are selected to distinguish them in appearancefrom the background environments in which they are used. Devices foridentifying or extracting data from optical codes are sometimes referredto as “optical code readers” of which bar code scanners are one type.Optical code readers are used in both fixed and portable installationsin many diverse environments such as in stores for checkout services, inmanufacturing locations for work flow and inventory control and intransport vehicles for tracking package handling. The optical code canbe used as a rapid, generalized means of data entry, for example, byreading a target bar code from a printed listing of many bar codes. Insome uses, the optical code reader is connected to a portable dataprocessing device or a data collection and transmission device.Frequently, the optical code reader includes a handheld sensor which ismanually directed at a target code.

Most conventional code readers are designed to read one-dimensional barcode symbols. The bar code is a pattern of variable-width rectangularbars separated by fixed or variable width spaces. The bars and spaceshave different light reflecting characteristics. One example of aone-dimensional bar code is the UPC/EAN code used to identify, forexample, product inventory.

Bar codes can be read employing solid state imaging devices. Forexample, an image sensor may be employed which has a two-dimensionalarray of cells or photo sensors which correspond to image elements orpixels in a field of view of the device. Such an image sensor may be atwo-dimensional or area charge coupled device (CCD) and associatedcircuits for producing electronic signals corresponding to atwo-dimensional array of pixel information for a field of view. Aone-dimensional linear array of photodiodes is also known for use indetecting a bar code reflection image, for example, U.S. Pat. No.6,138,915 to Danielson, et al., which is herein expressly incorporatedby reference.

It is known in the art to use a CCD image sensor and objective lensassembly in an optical code reader. In the past, such systems haveemployed complex objective lens assemblies originally designed forrelatively expensive video imaging systems. Such systems may have asingle sharp focus and a limited depth of field, which along withconventional aiming, illumination and signal processing and decodingalgorithms, limits the versatility and working range of the system.

Other known imaging systems are designed primarily for reading opticalcodes. Such reading systems involve the assembly and alignment ofseveral small parts. These parts may include a lens, an aperture and a2D image sensor array such as a CCD chip. Such a structure isillustrated, for example, in WO 99/64980 which is hereby incorporated byreference herein. A miniature imager adapted for use in a hand mountedcode reader is disclosed in U.S. patent application Ser. No. 09/684,514filed Oct. 10, 2000 to Patel, et al., which is herein expresslyincorporated by reference.

The design of an imaging system is dependent upon the size of thepackage in which the imaging system is to be manufactured. Conventionalimaging systems which utilize off-the-shelf components are difficult tominiaturize due to the limited selection of off-the-shelf components.Further, due to various optical phenomena in the design of a miniatureimager, various tradeoffs between a component size and the quality of ascanned image must be weighed in the selection of components.Additionally, the selection of certain components for an imager may, dueto optical phenomena, limit the choice of other components for theminiature imager.

SUMMARY OF THE INVENTION OBJECTS OF THE INVENTION

Accordingly, it is an object of the present invention to provide asemiconductor device for imaging optical code symbols, and a bar codereader including such semiconductor device.

It is a further object of the present invention to provide asemiconductor device which provides an adequate scanned image whileminimizing the physical size and shape, i.e., the form factor, of thedevice.

A semiconductor device for imaging optical code symbols is typicallyused in portable applications where the semiconductor device isincorporated into a handheld device. These handheld devices typicallyhave a limited battery capacity.

It is an object of the present invention to provide a semiconductordevice adapted for imaging bar code symbols which uses a minimum amountof power in the capture and processing of an image.

Conventional imaging systems which employ solid state imagers sufferfrom a limitation on the distance that a target image can be from thelens of the imager for correct decoding of the target imager.Specifically, in conventional imaging systems the plane of the pixelarray of the solid state imager is arranged perpendicular to the opticalaxis of the focusing lens. Accordingly, the pixels of the solid stateimager are all focused on the same spatial plane of the target image.

All of the pixels being focused on the same spatial plane severelylimits the working range, i.e., the distance between the imaging systemand the target image, of the imaging system. If a conventional imagingsystem has a single fixed focus lens, adjustments between the imagingsystem and the target image may have to be made in order to properlyreceive and decode the target image.

To provide illumination and to assist in aiming, imaging systems canemploy either lasers or light emitting diodes (LEDs). LEDs may bepreferred over lasers since the incoherent nature of the LED lightsource does not produce the speckle noise impact that is produced bylasers. Further, LEDs are more cost effective than lasers due to theease of manufacturing and packing of LEDs. Additionally, LEDs can bebuilt more compactly and are easier to surface mount than lasers.However, compared to lasers, LEDs are not an ideal point source.Specifically, light produced by an LED is less focused which produces anincreased line thickness of the projected light. To reduce the linethickness of the light produced by an LED, many designers place amechanical slit in front of the LED. However, the mechanical slitreduces the amount of light that is projected by the LED onto an object.

The objects and features of the invention will be apparent from thiswritten description and drawings.

FEATURES OF THE INVENTION

These and other problems, drawbacks and limitations of conventionaltechniques are overcome according to the present invention by asemiconductor device for imaging optical code symbols, in particular barcode symbols, as set forth herein, and by a bar code reader as set forthherein. Preferred embodiments of the present invention are set forthherein.

In a miniature imager which may be used in connection with the presentinvention, the pixel width or pitch of an imaging array is reducedcompared to a larger sized imager while maintaining the instantaneousfield of view of each pixel and the area of the aperture compared tolarger sized imagers. In accordance with this embodiment an imager witha 4 μm pixel width or pitch can be produced with a detector array lengthless than or equal to 2 mm. In accordance with one aspect of thisembodiment, by staggering alternate rows of pixels by one half pixelrelative to each other a one-dimensional imager can be produced with apixel width or pitch of approximately 3 μm and a detector array lengthof approximately 0.75 mm.

In another embodiment, an imager is provided which has a very small formfactor and can be operated with little or no artificial illuminationprovided by the imager thereby providing very low power operation. Inaccordance with this embodiment, an imager chip is mounted on an imagerboard inside of an imager housing. The imager housing forms a dark roomaround the imager chip thereby enabling the imager to operate without anexternal seal. In accordance with one aspect of this embodiment, thesize of the aperture can be increased to thereby minimize and/oreliminate the need for the imaging engine to provide artificialillumination. In accordance with another aspect of this embodiment, alow noise imager with a gain is provided to reduce and/or eliminate theneed for the imaging engine to provide artificial illumination. Inaccordance with yet another aspect of this embodiment, an imager whichprovides a nonlinear response, such as a logarithmic imager, can beprovided to reduce and/or eliminate the need for the imaging engine toprovide artificial illumination.

In accordance with yet another embodiment, an imager includes an imagesensor and a focusing lens. The imager sensor has an array of pixels ina first plane and the focusing lens has an optical axis in a secondplane. The first and second planes are arranged such that they are notperpendicular to each other, thereby increasing the working range of theimager.

In accordance with another embodiment, a device includes a lightemitting diode having a square portion and a rectangular portion,wherein a height and a width of the rectangular portion is not equal toa height of the square portion. The device also includes a bonding pad,wherein the bonding pad is located on the square portion. In accordancewith one aspect of this embodiment, the light emitting diode alsoincludes a second square portion, wherein the rectangular portion has afirst and a second side the size of the height, wherein the squareportion is located on the first side of the rectangular portion and thesecond square portion is located on the second side of the rectangularportion. A second bonding pad is located on the second square portion.In accordance with another embodiment, a light emitting diode dieincludes a rectangular shaped light emitting diode with a bonding padsurrounding the light emitting diode.

The above described subject matter may further be defined as follows:

An imager comprises a solid state image sensor for producing electronicsignals corresponding to a target image, wherein the image sensorincludes an array with a number of pixels less than or equal to 1024pixels and each pixel has a width or pitch of less than or equal to 4μm; and an aperture for receiving light reflected from the target andfor passing the reflected light onto the image sensor, whereinpreferably the image sensor is a one-dimensional image sensor, thenumber of pixels is less than or equal to 1024 pixels and each pixel hasa width equal to 3 μm, whereby the length of the array is less than orequal to 1.5 millimeters, or wherein the number of pixels in the imagesensor is less than or equal to about 500 pixels, each pixel has a widthequal to 3 μm and wherein the pixels are arranged in two adjacent rows,one row offset by half of a pixel from the other, whereby the length ofthe array is less than or equal to 0.75 millimeters. Preferably, theabove image sensor is a two-dimensional image sensor, whereby the arrayis less than 2 millimeters in its longest length. In particular, theabove image sensor may be a CMOS detector array. The above image sensoris preferably adapted to be mounted on a printed circuit board usingre-flow soldering techniques. The above imager may further compriseillumination/aiming light emitting diodes; illumination/aiming lenses;and an imaging lens, wherein the imaging lens is placed in the aperture,wherein the apparatus is included in a molded package. Preferably, theimager has dimensions less than or equal to 5 millimeters by 3millimeters by 2.25 millimeters.

In another aspect, there is provided an imager comprising an imagerhousing which includes an imager chip; a lens, wherein the lens isincorporated into the imager housing opposite of the imager chip, andwherein the imaging housing has a volume less than or equal to 3.3 cm³(0.20 cubic inches). Preferably, the imager chip is enclosed in a darkroom, thereby enabling the imager to operate without an external seal.Advantageously, the maximum dimensions of the imager are 20.6×14.2×11.4mm³. In a preferred embodiment, the imaging housing further includes alight emitting device for illuminating a target image, and/or theimaging housing includes an aperture, wherein the size of the apertureis selected to enable scanning of a target image without illumination bythe imager. Preferably, the above imager chip is a low noise imager witha gain, thereby enabling scanning of a target image without illuminationby the imager. The above imager chip may be a logarithmic responseimager, thereby enhancing a contrast between dark portions and brightportions of a target image and thereby enabling scanning of a targetimage without illumination by the imager.

According to another aspect, there is provided an imager comprising animager housing which includes an imager chip; and a lens, wherein thelens is incorporated into the imager housing opposite of the imagerchip, and wherein the imager chip is a low noise imager which amplifiesthe imaged signals, thereby enabling scanning of a target image withoutillumination by the imager. Preferably, the imager housing has a volumeless than or equal to 3.3 cm³ (0.20 cubic inches).

Still further, there is provided an imager comprising an imager housingwhich includes an imager chip; and a lens, wherein the lens isincorporated into the imager housing opposite the imager chip, andwherein the imager chip provides a nonlinear intensity response to lightreflection to the chip by a target image, thereby enabling scanning ofthe target image without illumination by the imager, wherein preferablythe nonlinear representation is a logarithmic representation of thetarget image. Here also, the imager housing preferably has a volume lessthan or equal to 3.3 cm³ (0.20 cubic inches).

According to still another aspect, there is provided an imagercomprising an imaging sensor mounted on a printed circuit board; and anaperture, wherein the imager has a volume less than or equal to 3.3 cm³.Preferably, the dimensions of the imager are equal to or less than 20.6by 14.2 by 11.4 millimeters. The imager may further comprise lightemitting diodes to provide illumination of a target image, and/or lightemitting diodes to illuminate a target on the target image to aid inaiming the imager.

Further, there is provided an imager comprising a two-dimensional imagesensor including a portion with horizontal rows of image elements in afirst plane; and focusing optics having an optical axis, wherein theimage sensor is oriented so that the first plane is not perpendicular tothe optical axis and so that different focal distances are provided fordifferent rows of image elements. Preferably, the focusing opticsinclude an objective lens symmetrically containing a plane substantiallynon-parallel to the first plane. The imager may further comprise lightemitting diodes to provide illumination of a target image.

According to another aspect, there is provided a device comprising alight emitting diode having a square portion and a rectangular portion,wherein a height and a width of the rectangular portion is not equal toa height of the square portion; and a bonding pad, wherein the bondingpad is located on the square portion. In a specific embodiment, therectangular portion preferably has a first and a second side the size ofthe height, wherein the light emitting diode further comprises a secondsquare portion, wherein the square portion is located on the first sideof the rectangular portion and the second square portion is located onthe second side of the rectangular portion, and wherein a second bondingpad is located on the second square portion.

Also, there is provided a device comprising a rectangular light emittingdiode; and a bonding pad, wherein the bonding pad surrounds the lightemitting diode, thereby providing a uniform light power emitted from thelight emitting diode.

According to the present invention, there is provided a semiconductordevice for imaging optical code symbols, comprising no more than 1024pixels, wherein each of the pixels has an aspect ratio that is greaterthan 2 to 1 with a short dimension not greater than 4 μm, and not lessthan 2 μm, wherein preferably the pixels are arranged in a single row.Moreover, the semiconductor device may have a collection surfaceconfigured as a set of not less than 256 and no more than 1024 pixels.

According to another aspect of the present invention, there is provideda bar code reader including a sensor for imaging a field of view of thereader comprising a single semiconductor device as set forth above.

Also described herein is a miniature imager for reading target images.The optical and electrical systems of the miniature imager are optimizedto reduce one or more dimensions or the volume of the imager. Inaccordance with one embodiment, the pixel width or pitch and focallength are decreased from that of a larger imager to maintain acomparable field of view for each pixel. The decreased pixel width orpitch allows the area of the aperture and the instantaneous field ofview of the pixel to remain constant while decreasing the overall sizeof the imager. In other embodiments, apparatus and techniques areprovided which reduce and/or eliminate the need for illumination of atarget by the imager thereby reducing the overall power consumed by theimager and/or its overall size. An imager with an increased workingrange is provided, as is a light emitting diode which produces a lightwith reduced line thickness.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and advantages of the invention will be understood byreading the following detailed description in conjunction with thedrawings in which:

FIGS. 1A and 1B respectively illustrate a top view and a side view of aminiature imager;

FIGS. 2A-2C respectively illustrate a top, front and side view ofanother miniature imager;

FIG. 3 illustrates a further miniature imager;

FIG. 4 illustrates the electrical components of a miniature imager;

FIG. 5 illustrates an imager with an increased working range;

FIG. 6A illustrates a conventional LED;

FIG. 6B illustrates an LED which may be used together with the presentinvention;

FIG. 6C illustrates another LED which may be used together with thepresent invention;

FIG. 6D illustrates yet another LED which may be used together with thepresent invention;

FIG. 6E illustrates yet another LED which may be used together with thepresent invention; and

FIG. 7 illustrates a semiconductor device in accordance with the presentinvention.

DETAILED DESCRIPTION

In the following description, for purposes of explanation and notlimitation, specific details are set forth in order to provide athorough understanding of the present invention. However, it will beapparent to one skilled in the art that the present invention may bepracticed in other embodiments that depart from these specific details.In other instances, detailed descriptions of well-known methods,devices, and circuits are omitted so as not to obscure the descriptionof the present invention.

FIGS. 1A and 1B respectively illustrate a top view and a side view of aminiature imager. The imager is incorporated into a molded opticalpackage 110. Structures and techniques for so doing are disclosed inU.S. patent application Ser. No. 09/880,906, filed Jun. 15, 2001 to Mazzet al. entitled “Molded Imager Optical Package and Linear Detector-BasedScan Engines”, hereby expressly incorporated by reference. The moldedoptical package includes an imaging/decoder integrated circuit (IC) 120,illumination/aiming light emitting diodes (LEDs) 130, imaging lens 140and illumination/aiming lenses 150. In accordance with the preferredembodiment of the present invention, the imaging/decoder IC 120 isfabricated in accordance with known complementary metal oxidesemiconductor (CMOS) techniques. Alternatively, the imaging/decoder IC120 can comprise a CCD imager with associated decoding circuitry.

In operation, the imaging/decoder IC 120 receives an image via imaginglens 140. To assist in the decoding of the target image, illuminationLEDs 130 project light on the target image via illumination/aiminglenses 150. The location of the target image in the proper field of viewof the imaging/decoder IC is aided by projecting an aiming pattern onthe target image using illumination/aiming LEDs 130. Illumination/aimingLEDs are focused on a target image through illumination/aiming lenses150. It will be recognized that the illumination/aiming lenses 150 canbe designed such that the light from illumination/aiming LEDs arescattered in any known target pattern on the target image.

The volume of the imaging system is scaled by scaling the pixel width orpitch of the detector array of imaging/decoder IC 120. It will berecognized that the pixel width or pitch refers to the spacing betweenimage elements, i.e., pixels, on an image sensor. When the pixel widthor pitch is decreased the focal length is decreased to maintain acomparable field of view. If the aperture size is kept constant, thenthe same amount of light is collected per pixel and there is not a lossin imager sensitivity. If the size of the aperture is not limiting thesize of the imager, then in a 2D imaging system all three dimensionsscale by the scale factor of the pixel. In a 1D imaging system twodimensions scale by the scale factor of the pixel.

The imaging engine is designed to provide a similar depth of focus andsimilar light throughput for each pixel. This results in a sacrifice ofthe pixel dynamic range and pixel quantum efficiency. The effect onpixel dynamic range is first order, but dynamic range is not veryimportant for applications such as bar code imaging. The effect on pixelquantum efficiency is second order for relatively large pixels, forexample, greater than 5.

It will be recognized that the light collected by an optical system froma point source is given by the equation:$\frac{A_{aperture}}{{\pi s}^{2}}$

In this equation, A_(aperture) is the area of the aperture and s is thedistance to the source. By integrating over the instantaneous field ofview of a single pixel the amount of light collected by the pixel isgiven by the equation: $\frac{A_{aperture}}{{\pi s}^{2}}A_{pixelFOV}$

When the pixel pitch or width of an imaging system is reduced, the areaof the aperture (A_(aperture)) and the instantaneous field of view ofthe pixel (A_(pixelFOV)) can be kept constant while maintaining thedepth of focus. This ensures that in the object space everything, i.e.,aperture size, nominal focal distance, field of view and instantaneousfield of view of each pixel, is the same when the sensor size isreduced. Thus, the size of the imaging engine can be scaled withpractically no impact on bar code reading performance.

In view of the discussion above, the miniature imager illustrated inFIGS. 1A and 1B has a CMOS detector array with a 4 μm pitch and 512pixels. This results in an advantageously small detector length ofapproximately 2 mm. The focal length of the system is approximately 3mm. Accordingly, the overall dimensions of the scan engine illustratedin FIGS. 1A and 1B can be on the order of 5×3×2.25 mm³.

The practical limit for pixel width or pitch is approximately 3 μm. In1D systems the detector footprint can be further minimized by making twoor more rows of pixels offset, e. g., staggered, from one another. Forexample, an array of 500 pixels with 3 μm pitch has a length of 1.5 mm.By laying out the array as two adjacent rows offset by half of a pixel,the pixel width or pitch is maintained at 3 μm, but the detector arrayhas a resultant length of 0.75 mm. Since the arrays are offset by halfof a pixel, the pixel values can be combined to obtain a resolutionequivalent to a 1.5 μm pixel. The pixel width or pitch is maintained ata reasonable level for absorbing photons, but the detector footprint,and thus, the total volume of the system can be dramatically decreased.

The imaging detector array, read-out electronics, analog-to-digitalconverter and decoding logic may all be integrated into a single chip.The imaging/decoding chip is mounted on a carrier with two LED die or asmall laser. The carrier can be an FR4 substrate, an industry recognizedorganic substrate, and contain a lead frame or solder bumps forattachment to a larger circuit board. The carrier is covered with amolded plastic piece that has the optical surfaces molded into it. Themolded plastic cover is optical quality and can tolerate temperaturesencountered in automated circuit board assembly. The device is acomplete scanner, including opto-mechanics and electronics and can behandled like a surface mount integrated circuit and is compatible withre-flow soldering techniques. The device as illustrated in FIGS. 1A and1B is a complete imager that can be mechanically attached to a circuitboard by solder joints only. Accordingly, the miniature imagerillustrated in FIGS. 1A and 1B does not require screws or any similarmechanical support, thus reducing the size and complexity of a devicewhich incorporates this imaging engine.

FIGS. 2A-2C respectively illustrate a top, front and side view ofanother miniature imager. The miniature imager illustrated in FIGS. 2A-Chas a very small form factor and can be operated with little or noartificial illumination for very low power operation. The miniatureimager includes imager housing 210 which can be made of any number ofavailable metallic or plastic materials which are known to those skilledin the art. Inside of imager housing 210, imager chip 220 is mounted animager board 230 using any one of the available bonding and mountingtechniques. Additionally, the imager chip 220 can be mounted on imagerboard 230 using chip-on-board technology. The imager chip 220 isarranged in imager housing 210 directly behind lens 240. Lens 240 can bemade of any suitable transparent material. The imager chip is enclosedin a dark room 250, which is formed within imager housing 210, to enablethe imager chip 220 to operate without an external seal and whichsimplifies the design of the host device, e.g., camera, terminal ormicrocomputer.

To achieve contrast in the scene captured by imager chip 220, LEDs 260can be provided. LEDs 260 can either be discrete or integrated as anarray. Further optics for dispersing the light, if necessary, can beplaced in the imager housing 210 for illumination of the scene.Alternatively, to achieve contrast in the scene captured by imager chip220 the size of the aperture can be increased. The increase in the sizeof the aperture will result in a reduced working range but may reducepower usage by minimizing or eliminating the need to illuminate a targetimage.

A further alternative to achieve contrast in the scene captured byimager chip 220 can be through the use of a low noise imager with a gainor through the use of a logarithmic response imager. If the noise floorof the imager is below the quantization level of the analog-to-digitalconverter, then the analog signal can be amplified to increase thecontrast of images captured with small amounts of light. A nonlineartransformation, such as a logarithmic one, can be used to enhancecontrast between dark parts of the images with little effect on thebright parts. Additionally, any of the above techniques for achievingcontrast can be combined to improve the response of the imager.Automatic gain control can be used to achieve a wide intrascene dynamicrange.

It should be recognized that the imager illustrated in FIGS. 2A-C can befurther modified from that illustrated in the figures. It will be notedthat lens 240 is no essential component and may be omitted and/or otheroptical components may be used together with or instead of lens 240. Forexample, the optical housing can contain one or more mirrors to directlight on the imager chip to help improve contrast in the scene. Further,the optical housing can contain a prism or other diffractive element todirect light onto the imager chip 220. Additionally, the imager cancontain a motor for inserting a clear piece of plastic or glass into theoptical path between the lens and the imager, which results in focusingthe lens to two different positions. To reduce the cost of the imagerhousing and lens, these components can be made of molded plastic.Further, a screen used in the mold could form the dark room and lensaperture.

Accordingly, the miniature imager illustrated in FIGS. 2A-2C can be of asmall form factor, e.g., SE900 form factor, with maximum dimensions ofapproximately 20.6×14.2×11.4 mm³ (0.811×0.559×0.449 inches), resultingin a volume of the imager of 3.3 cm³ (0.20 cubic inches). The SE900 formfactor is a form factor which is used in the imager industry for themanufacture of imaging devices. The imager contains optics andelectronics sufficient to produce a signal stream, either analog ordigital, to a connected microcomputer or display. The imager of theimaging chip 220 can be either CCD or CMOS.

FIG. 3 illustrates another miniature imager. The miniature imagerillustrated in FIG. 3 includes an imager housing 310. Inside imagerhousing 310 is an image sensor 320 attached to a printed circuit board330. The image sensor 320 may be a CMOS image sensor. The printedcircuit board is provided near or at the rear of the imager housing 310.An aperture 340 is incorporated into the imager housing 310 so as toallow the image sensor 320 to capture a scene. The front face of theimager housing 310 includes a plurality of LEDs 350 for sceneillumination and for aiming. It will be recognized that the layout ofthe LEDs 350 on the front face of the imager housing can be of any knowndesign that is intended to illuminate a target and to provide assistanceto a user aiming a device which incorporates the imager of FIG. 3. Thedimensions of the imager of FIG. 3 are approximately 20.6×14.2×11.4 mm³(width/depth/height), resulting in a volume of the imager ofapproximately 3.3 cm³ (0.20 cubic inches). Of course, smaller dimensionsare possible, for example if a smaller number of pixels or smaller pixelwidth is used.

FIG. 4 illustrates the electronics of a miniature imager. The imager ofFIG. 4 includes a 2D area sensor 410 which is controlled via clockdriver and charge pump 420. Clock driver and charge pump 420 iscontrolled in accordance with signals received from timing generator430. An image captured by 2D area sensor 410 is provided to correlateddouble sampling block (CDS) 440. Since pixels do not always return tothe same value when they are reset, correlated double sampling is usedto remove the offset introduced by pixels which have not returned totheir normal reset values. Accordingly, correlated double samplinginvolves capturing two values of the pixels. The first value is thevalue of the pixels with the desired image, e.g., a bar code, and thesecond value is the value of the pixels after being reset. The twovalues of each pixel are compared to remove the offset introduced bypixels which have not returned to their normal reset value. Afterperforming the correlated double sampling, the image is passed through aweak AC coupling to block DC content of the correlated double sampledimage. After the weak AC coupling an automatic gain control (AGC) 442amplifies the signal which is then provided to an analog-to-digitalconverter 444. In accordance with a preferred embodiment of the presentinvention, the analog-to-digital converter 444 is a 9 bitanalog-to-digital converter.

Digital data is provided by the analog-to-digital converter 444 to theglue logic field programmable gate array (FPGA) block 450. The gluelogic/FPGA 450 packs the digital data so that it can be read bymicroprocessor 460 and connects with the microprocessor 460 to provideall of the camera controls. The microprocessor 460 includes DRAMembedded on the same IC as the microprocessor which increases the speedof the system while allowing a reduced size and cost for the resultantimager. The microprocessor 460 operates under control of a programstored in flash memory 470 via an external data and address bus.

The target image can be illuminated using illumination module 475, whichin a preferred embodiment of the present invention is provided by 650 nmred LEDs. The LEDs are arranged so that the target image is uniformlyilluminated. To assist a user of the imager, aiming module 480 can beused to provide a unique aiming pattern. Aiming module 480 can include alaser diode and a diffractive optical element (DOE) to provide theunique aiming pattern. Interaction between the host device whichincorporates the miniature imager and the miniature imager is providedusing host interface 490. Since the imagers described herein areminiature, i.e., of a small form factor, the host device can be aportable radio telephone (cellular phone), a personal digital assistant(PDA), or the like. Using the elements described in connection with FIG.4 a miniature imager can be achieved which can be manufactured in aSE1223 form factor. The SE1223 form factor is a form factor which isused in the imager industry for the manufacture of imaging devices.

The working range of an imager may be increased by positioning a planeof the image sensor at an angle which is not perpendicular to theoptical axis of the focusing lens. FIG. 5 illustrates an imager with anincreased working range. Specifically, the imager includes an imagesensor 510 and a focusing lens 520. The image sensor comprises aplurality of horizontal rows of pixels facing the lens 520. Although notillustrated in FIG. 5, it will be recognized that the imager illustratedtherein may have additional components similar to those discussed abovewith respect to FIGS. 1-4.

As illustrated in FIG. 5, a plane parallel to the front of the pixels ofimager 510 is tilted at an angle θ with respect to the optical axis offocusing lens 520. Accordingly, for example, one horizontal pixel row PR1 of the imager 510 is focused at first spatial plane 1′ and anotherhorizontal pixel row PR 2 is focused at a second spatial plane 2′,different from the first spatial plane 1′. By placing the image sensorsof imager 510 at a non-perpendicular angle θ with respect to the opticalaxis OA of the focusing lens 520, the imager is able to read and decodetarget images which are at various distances from the imager byinterrogating each of the horizontal rows of pixels which are focused atdifferent spatial planes. The ability to read and decode target imageswhich are at various distances reduces user frustration from having tomanually adjust the distance between the imager and the target image tosuccessfully read and decode the target image. The imager illustrated inFIG. 5 can be used for reading one-dimensional or two-dimensional barcodes in either a manual or automatic mode.

FIG. 6A illustrates a top view of a conventional LED. The LED 600includes a bonding pad 610 through which electrical power is supplied tothe LED 600. Conventional LEDs, such as the one illustrated in FIG. 6A,have a square shape with dimensions of approximately 350 μm by 350 μm.As illustrated in FIG. 6A, the bonding pad 610 is typically placed inthe middle of the LED 600. This placement of the bonding pad 610 blocksapproximately 30% of the light power emitting from the LED 600.Moreover, as discussed above, conventional LEDs produce less focusedlight than lasers, the result of which is projected light with anincreased line thickness.

FIGS. 6B-6E illustrate three different embodiments of novel LEDs.Generally, the novel LEDs have a die area which is almost the same asthe die area of conventional LEDs, thereby maintaining substantially thesame emitting power as conventional LEDs. However, the novel LED die isthinned in the focusing direction, i.e., the direction which producesthe line thickness, and elongated in another direction. Referring now toFIG. 6B, the LED 615 has a square portion 620 and an elongatedrectangular portion 625. More generally and in other words, the novelLED has at least one main portion having a bonding pad and an elongatedportion extending from the main portion. It is not necessary that themain portion has a square shape and the elongated portion isrectangular; for example, the corners in the embodiment of FIG. 6B couldbe rounded. Referring again to FIG. 6B, the square portion 620 has abonding pad 630. As indicated in the FIG. 6B, the LED 620 has dimensionsof D_(x) by D_(y), wherein D_(y) is the width of the elongated portion625. Since the voltage which drives the LED is supplied via the bondingpad, the amount of light power emitting from the LED decreases thefurther the portion of the LED is from the bonding pad. Accordingly, inFIG. 6B, the amount of light power emitted from portions of theelongated portion 625 decreases for portions further to the right of thebonding pad 630.

FIG. 6C illustrates a top view of another novel LED. Specifically, theLED 635 has two square portions 640 and 647 joined by a rectangularportion 642. Square portion 640 has a bonding pad 645 located thereonand square portion 647 has bonding pad 650 located thereon. By placingbonding pads 645 and 650 on each side of the rectangular portion 642, amore uniform amount of light power emitted from the rectangular portionis achieved compared to the LED 615 illustrated in FIG. 6B.

FIG. 6D illustrates a top view of yet another novel LED. A bonding pad670 is placed adjacent to the rectangular portion 660 of LED 655.

Accordingly, the bonding pad 670 does not block any light emitted fromthe elongated portion. Moreover, whereas the placement of the bondingpad in FIG. 6C may result in a reduced amount of light in the center ofthe rectangular portion, the placement of the bonding pad 670 in FIG. 6Densures a more uniform distribution of light emitted from the center ofthe rectangular portion 660 of LED die 655.

FIG. 6E illustrates a top view of yet another novel LED. A rectangularportion 680 of the LED die 675 is surrounded on all sides by a bondingpad 685. By surrounding the rectangular portion 680 of the LED die 675by the bonding pad 685, a uniform distribution of light emitted from thewhole rectangular portion 680 of the LED die 675 is achieved compared tothe LED dies illustrated in FIGS. 6B-6D. In accordance with oneembodiment of the present invention, D_(y) in FIGS. 6B-6D can be lessthan or equal to 50 μm. To maintain the same emitting power asconventional LEDs, D_(x) in FIGS. 6B-6E is selected such that the diearea of the LED is the same as the die area of conventional LEDs.

FIG. 7 is a highly schematic illustration of a semiconductor device 1for imaging optical code symbols, in particular bar code symbols, inaccordance with the present invention. This semiconductor device mayfind preferred application as a sensor for imaging a field of view of abar code reader, and may be used together with some or all of theelements described above, such as in a miniature imager, together withthe above described LEDs, and so forth.

The semiconductor device 1 comprises no more than 1024 pixels 2.Preferably, the number of pixels is between 256 and 1024. A preferredembodiment may comprise, for example, 512 pixels. The pixels, 2 eachhave an aspect ratio that is greater than 2 to 1 with a short dimensionnot greater than 4 μm and not less than 2 μm. While it is generallypossible to provide the pixels, e. g., in staggering alternate rows ofpixels by one half pixel relative to each other as described above, itis presently preferred to arrange the pixels in a single row as shown inFIG. 7. As is clear from the FIG. 7, the pixels are arranged with thelong dimension perpendicular to the row, and with the row being formedwith the short dimensions of the pixels being placed adjacent to eachother. An aspect ratio of the pixels of more than 2 to 1 will providesuperior results for the semiconductor device in reading bar codesymbols since the bars and intermediate spaces of the bar code symbolsmay be well distinguished despite the small size of the semiconductordevice.

Such a semiconductor device as described above may form a sensor forimaging a field of view in a bar code reader. Such a sensor isparticularly small, but is still capable of reliably imaging a bar codesymbol. Since a single semiconductor device of the present invention issufficient for imaging a bar code symbol, the sensor (and, thus, the barcode reader) may be extraordinarily small which is particularly usefulfor portable and/or miniature applications of a bar code reader.

The present invention has been described with reference to an exemplaryembodiment. However, it will be readily apparent to those skilled in theart that it is possible to embody the invention in specific forms otherthan that of the exemplary embodiment described above. This may be donewithout departing from the scope of the invention as defined by theappended claims.

1. A bar code reader for reading a symbol having bars spaced apart alonga longitudinal direction, each bar extending lengthwise along atransverse direction perpendicular to the longitudinal direction,comprising: a sensor for imaging a field of view of the reader, thesensor comprising a single semiconductor chip having no more than 1024pixels arranged along a row having a length not exceeding 2 millimeters,each of the pixels having a long dimension, a short dimension, and anaspect ratio that is greater than 2 to 1, the short dimension of eachpixel being not greater than 4 μm and not less than 2 μm; and a packagesupporting the chip, the package occupying a volume of no more than 3.3cubic centimeters.
 2. The reader as defined in claim 1, wherein thevolume measures approximately 20.6 mm by 14.2 mm by 11.4 mm.